Air Pressure and Wind Flashcards
What is air pressure do?
- Controls all air movement in the atmosphere
- Air (wind) moves from areas of high to low pressure
- Hourly variations in air pressure give strong indications of weather in the next few hours
- Works in all directions
What is the weight of the atmosphere over a square inch of the Earth’s surface at sea level?
14.7 lbs per square inch
How does a mercury barometer work?
- 1643: barometer invented by Evangelista Torricelli:
- Mercury vapor is more dangerous
- Placed a glass cylinder inside the vat of mercury
- Lifts it up and places it in upright
- Mercury fell down cylinder and stopped close to top
- Water will do the same thing, but the barometer would have to 13.5 times bigger to account for the 14.7 pounds of water
- The higher the mercury goes up, the higher the pressure is
- The lower the mercury level is, the lower the pressure is
How does air pressure change with height?
Decreases
How does air pressure change as temperature changes?
Colder air indicates high pressure because it is denser than warm air, which indicates low pressure
How does air pressure change as specific humidity changes?
- Air pressure decreases with increasing specific humidity
- Increases with decreasing specific humidity because water is a light molecule
What kind of weather is associated with high and low pressure?
High pressure: sunny weather
Low pressure: rainy weather and clouds
What makes the wind blow?
If isobars are closer together, wind wants to go go from areas of high pressure to low areas of low pressure
What is pressure gradient force and how is it responsible for wind currents?
This force moves air from high to low pressure, creating wind currents
What two things control the direction of the wind?
Pressure gradient force and the Coriolis effect
What causes the Coriolis effect?
- Related to the rotation of the Earth
- Air is deflected to the right as it moves across the surface of the Earth in the northern hemisphere
- Deflected to the left in the southern hemisphere
How does the Coriolis effect affect the direction of wind movement? (for N and S)
NORTHERN HEMISPHERE:
1) Wind movement: right
2) High pressure system: right (clockwise)
3) Low pressure system: left (counterclockwise)
SOUTHERN HEMISPHERE:
1) Wind movement: left
2) High pressure system: left (counterclockwise)
3) Low pressure system: right (clockwise)
How does the Coriolis effect affect the movement of warm and cold water currents in the ocean?
Northern Hemisphere: currents move right (clockwise)
Southern Hemisphere: currents move left (counter-clockwise).
In what direction would the winds blow if the Earth were not rotating?
- Winds would blow toward the equator
- They would blow south in the Northern Hemisphere
- North in the Southern Hemisphere
In air pressure belts:
when is air rising or falling?
when is air pressure high or low?
- Air rises at lows, and falls at highs
- Air pressure is high when an area is below sinking air, and low when an area is below rising air
Why is the Intertropical Convergence Zone an area of high rainfall?
- The air there is warm, and warm air has a lower density, so it rises
- Rising air creates clouds, and causes rain
Why are areas of the Earth’s surface at around 30 degrees N and 30 degrees S zones of relatively high air pressure and low rainfall?
- Smaller circle around 30 than at the equator
- Air from equator bent right/left, doesn’t reach poles, stops at 30 degrees
- Cold air sinks over these areas, which is denser than warm air, sinking air inhibits clouds
What are the changes in meteorological data that occur as a front passes through an area? (Cold front)
Cold front passing through:
Warm»_space;> cold
Moist»_space;> dry
Low air pressure»_space;> high air pressure
Where are the wind belts: trade winds, westerlies, and polar easterlies?
90-60 N: Polar North-Easterlies 60-30 N: Prevailing South-Westerlies 30-0 N: Northeasterly Trade Winds 0-30 S: Southeasterly Trade Winds 30-60 S: Prevailing North-Westerlies 60-90 S: Polar South-Easterlies
Where are the different air pressure belts on a map of the world (Intertropical Convergence Zone, polar highs, subtropical highs, and subpolar lows)?
0: Intertropical Convergence Zone
30: Sub-Tropical High
60: Sub-Polar Low
90: Polar Hugh
Coriolis Effect
- As the Earth rotates, air is deflected to the right as it moves across the surface of the Earth in the northern hemisphere
- Deflected to the left in the southern hemisphere
Doldrums
Refers to the ITCZ where ships can get stuck in windless waters
Easterlies
Winds in the polar regions that blow from the east
Gyre
- A circular pattern of ocean currents
- Clockwise in the Northern Hemisphere
- Counterclockwise in the Southern Hemisphere
- Warm water current- gulf stream
- Circular because of the wind belts
- Garbage collects in center of gyre
Horse Latitudes
30 degrees north and south of the equator, where there can be windless waters
Intertropical Convergence Zone (ITCZ)
On the equator, where warm air rises, creating an area of low pressure
Isobar
- Iso means same
- Lines on a weather map that connect areas of equal air pressure
- Exists every 4 millibars, in multiples of four, to show air pressure
Millibar
Used to measure barometric pressure on a map
Pressure Gradient Force
Air moves from areas of high to low pressure, creating wind currents
Trade Winds
- Steady winds blowing northeast in the Northern Hemisphere
- Southeast in the Southern Hemisphere
- Located above and below the ITCZ
Westerlies
Wind between the trade winds and polar easterlies that blow to the west
Wind
Movement of the air, especially in the form of a current of air blowing from a particular direction
Why is the atmosphere so spread out?
All the molecules move around and the force of collisions push the molecules out
Oxygen
- In a cubic cm of air: 24 sextillion molecules of air
- O2 molecule = 425 meters / second
- On average each molecules experiences 6.6 billion collisions per second
- In intergalactic space: there is 1 atom per cubic meter and experiences 1 collision every 2.9 billion years
Air pressure
- The weight of the atmosphere over a specified area of the Earth’s surface
- Gravitational component and the force of colliding air molecules component
1) Global Wind that moves weather across US
2) Warmest Global Wind air
1) Prevailing South-Westerlies
2) Trade Winds
What causes changes in air pressure?
1) Entry into your area of an air mass with higher or lower air pressure
2) Temperature (colder = denser = higher air pressure)
3) Changes in specific humidity (adding a light element (water), amount of heavy molecules going down, humid day = low air pressure)
Average sea level air pressure in:
1) pounds / square inch
2) millibars
3) g /cm
4) kg / square cm
5) torr
1) 14.7 pounds / square in
2) 1013.25 millibars
3) 1013.25 g / cm
4) 1.01325 kg / square cm
5) 760 torr
Average air pressure of mercury (inches, torr, millibars)
29.92 inches
760 mm = 760 torr
1013.25 millibars
What are the factors that determine how fast winds move by pressure gradient force?
1) How far apart the areas of high and low pressure are (closer = faster)
2) The difference in pressure between the high and low pressure areas (greater difference = faster)
Why does Europe have milder winters?
-Paris much high latitude than us but they have milder winters
-Gulf stream brings warm water to Europe
Westerly wind belt blows the warm air away from us
What is the boundary between polar easterlies / westerlies like?
- Wavy, climate very changeable
- Jet stream flows along this boundary, propelling low pressure systems
Moon phase
Waxing crescent
